This simulation models how edge and screw dislocations glide through a crystalline lattice under applied shear stress, producing plastic deformation at the atomic scale. The elastic strain field around each dislocation is computed from the standard isotropic continuum solution — compressive above the slip plane and tensile below — revealing why the ⊥ symbol marks a region of concentrated stress. Users can observe that once the applied stress exceeds the critical yield stress, the dislocation glides one Burgers-vector step at a time, depositing permanent slip with each transit.
Dislocation slip is the dominant deformation mechanism in structural metals such as iron, aluminium, copper and titanium, and understanding it underpins the design of high-strength alloys, work-hardening schedules and fatigue-life predictions in aerospace, civil and automotive engineering.
An edge dislocation is a line defect in a crystal created by the edge of an extra half-plane of atoms inserted into the lattice. Atoms above the slip plane are compressed together while those below are pulled apart, storing elastic energy. Because only a small number of bonds along the dislocation line need to shift at any one moment, glide requires far less stress than simultaneously breaking all bonds across an entire slip plane.
Select a dislocation mode (Edge, Screw or Multi) using the buttons in the left panel, then raise the Applied Stress slider above the Yield Stress value to trigger automatic glide — the ⊥ symbol will traverse the lattice from left to right. You can also click "Apply Slip" to force a single glide event regardless of stress. Watch the stress-strain chart on the right update in real time and the Slip Events counter increment with each transit. Increasing Temperature activates thermally assisted glide even below the yield threshold.
The Burgers vector b is the magnitude and direction of the lattice displacement produced by one complete dislocation glide event — it is the "unit of slip." For face-centred cubic metals like copper or aluminium, |b| is approximately 0.25 nm (one nearest-neighbour distance); for body-centred cubic iron it is about 0.25 nm as well. In the simulation the Lattice Spacing slider scales |b| from roughly 0.10 nm to 0.50 nm, and the live Burgers |b| readout updates accordingly.
The theoretical shear strength of a perfect crystal is approximately G/2pi (where G is the shear modulus), giving values on the order of 1-10 GPa for common metals. Real metals yield at 10-500 MPa because dislocations allow deformation to propagate sequentially — analogous to moving a heavy rug by flicking a wrinkle across it rather than sliding the whole rug at once. This dislocation mechanism reduces the required stress by two to three orders of magnitude and is the reason engineering metals are ductile rather than brittle.
Cold rolling, wire drawing and forging all exploit dislocation slip to shape metals without fracture. Work-hardening deliberately multiplies the dislocation density until dislocations tangle and block each other, raising yield strength — for example, cold-drawn steel wire can reach 2 GPa, compared to around 250 MPa for the same steel annealed. Precipitation hardening in aluminium alloys (used in aircraft skins) pins dislocations on fine particles of Al2Cu or MgZn2, blocking glide and increasing strength by a factor of three to five.
Yes — this is one of the most widespread misconceptions in introductory materials science. Single crystals of metals such as copper or gold are extremely soft and ductile precisely because dislocations can glide freely; a single crystal of copper can be stretched to many times its original length without fracture. Brittleness in ceramics and ionic crystals arises because their slip systems are geometrically constrained and dislocation motion is impeded by electrostatic forces between unlike ions, not because crystallinity itself causes brittleness.
The dislocation concept was proposed independently and almost simultaneously in 1934 by Geoffrey Taylor (Cambridge), Egon Orowan (Berlin/Cambridge) and Michael Polanyi (Berlin), each seeking to explain the large gap between theoretical and measured crystal strengths. Direct experimental confirmation came in 1956 when Peter Hirsch and colleagues at Cambridge used transmission electron microscopy (TEM) to image individual dislocations moving in aluminium foil in real time — a landmark observation that validated a 22-year-old hypothesis.
Cyclic loading drives dislocations back and forth along the same slip band, eventually forming persistent slip bands (PSBs) that extrude micro-ridges and intrude micro-crevices at the surface. These surface intrusions act as stress concentrators and nucleate fatigue cracks, which then grow via dislocation emission at the crack tip. This is why polished and electroplated surfaces — which suppress slip-band emergence — dramatically extend the fatigue life of aircraft components such as landing-gear struts and turbine discs.
Current research focuses on several interrelated challenges: atomistic and molecular-dynamics simulations using machine-learned interatomic potentials aim to capture dislocation-solute and dislocation-precipitate interactions at nanosecond timescales; discrete dislocation dynamics (DDD) codes model the collective evolution of millions of dislocation segments to predict macroscopic flow; and in-situ synchrotron X-ray diffraction combined with high-energy electron diffraction enables strain mapping around individual dislocations in operating devices. High-entropy alloys (multi-principal-element alloys) represent a new paradigm where chemical disorder profoundly changes dislocation core structure and mobility, opening routes to unprecedented strength-ductility combinations.
A slip system is the combination of a specific crystallographic slip plane and the slip direction (Burgers vector) within that plane. Slip occurs on the most densely packed planes in the most closely packed directions because these require the least atomic rearrangement energy. Face-centred cubic (FCC) metals such as aluminium and copper have 12 independent slip systems (four {111} planes, each with three <110> directions), giving them excellent ductility. Body-centred cubic (BCC) metals like iron have 48 possible systems but fewer with high Schmid factors, making them stronger but less ductile at low temperatures. Hexagonal close-packed (HCP) metals such as magnesium have only three easy basal slip systems, which is why they are brittle at room temperature and require elevated temperature or texture control to form.
This simulation visualises how dislocations glide through a crystal lattice to produce plastic deformation. Atoms are drawn as a grid distorted by the elastic strain field of an edge dislocation, computed from the classic isotropic continuum solution using a Poisson's ratio of 0.3. When the applied shear stress reaches the yield stress, the marked half-plane (⊥) glides one lattice spacing per step, leaving a permanent slip behind. It shows why metals deform at far lower stress than breaking every bond at once would demand.
An edge dislocation — an extra half-plane of atoms — moving through a lattice under shear. Atom positions are offset by the textbook edge-dislocation displacement field u_x = (b/2π)[θ + xy/(2(1−ν)r²)], and a colour map tints atoms teal in compression and orange in tension. A live stress–strain curve and a schematic diagram accompany the lattice.
Pick a Mode (Edge, Screw or Multi). Adjust sliders for applied stress σ (0–200 MPa), yield stress τ_c (20–180 MPa), temperature (0–1000 K) and lattice spacing a. Use Pause/Play, "Apply Slip" to force a glide event, and Reset. Results show status, dislocation position, Burgers vector magnitude and slip count.
The dislocation concept was proposed independently by Taylor, Orowan and Polanyi in 1934 to explain why real crystals yield at stresses roughly a thousand times lower than the theoretical ideal — but dislocations were not directly observed until transmission electron microscopy in the 1950s.
A dislocation is a line defect in a crystal where the regular arrangement of atoms is disrupted. An edge dislocation is the edge of an extra half-plane of atoms, marked here by the ⊥ symbol. Because only the atoms along this line need to rearrange at any instant, the crystal can deform by sliding rather than by breaking every bond simultaneously.
When the applied stress σ meets or exceeds the yield stress τ_c, the dislocation becomes active and glides along its slip plane, advancing one lattice column per step. Each time it exits the right edge it deposits a permanent unit of slip on that row and increments the slip count, then re-enters from the left to repeat the process.
Temperature controls thermally activated glide: even below the yield stress there is a small Arrhenius-style probability exp(−ΔE/kT) that a dislocation hops, so raising temperature lets slip occur sub-threshold. Lattice spacing a sets the displayed Burgers vector magnitude |b|, scaled to roughly 0.1–0.5 nm to match real metals.
The atom displacements use the standard isotropic elasticity solution for an edge dislocation with Poisson's ratio ν = 0.3, so the compression-above, tension-below pattern is qualitatively correct. The values are clamped and scaled for clear visualisation, and the screw mode is shown schematically rather than with its full out-of-plane field, so treat it as illustrative rather than quantitative.
Shearing a perfect crystal would require breaking every bond on a plane at once, giving a theoretical strength near G/2π. Dislocations let deformation proceed by moving one atomic row at a time, like sliding a ruck across a carpet, which lowers the required stress by about three orders of magnitude. This is the central insight of crystal plasticity and the reason metals are ductile.